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How is distance in light-years converted to years back in time?
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When I look at the Alnitak,the left most star of Orion's belt, it is 736 light years away. How could I convert this distance to an estimate of how long ago what I am seeing happened.
Would it be simply be 736 years ago?
Are there instances of when this isn't as straight forward?
distances space-time time
asked 6 hours ago
Gabriel Fair
1113
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up vote
2
down vote
favorite
When I look at the Alnitak,the left most star of Orion's belt, it is 736 light years away. How could I convert this distance to an estimate of how long ago what I am seeing happened.
Would it be simply be 736 years ago?
Are there instances of when this isn't as straight forward?
distances space-time time
asked 6 hours ago
Gabriel Fair
1113
New contributor
Gabriel Fair is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
For short distances (e.g. within our galaxy, or even within our local cluster of galaxies), this is an accurate method. It becomes inaccurate once the scale exceeds the point at which gravitational attraction is outweighed by the expansion of the Universe. As an extreme example, the Universe is roughly 46 billion light years in radius but light has only travelled for 13.8 billion years. Hopefully someone with greater expertise can post an answer about exactly how far away metric expansion of the universe becomes a significant factor.
– Chappo
3 hours ago
add a comment |Â
up vote
2
down vote
favorite
up vote
2
down vote
favorite
When I look at the Alnitak,the left most star of Orion's belt, it is 736 light years away. How could I convert this distance to an estimate of how long ago what I am seeing happened.
Would it be simply be 736 years ago?
Are there instances of when this isn't as straight forward?
distances space-time time
asked 6 hours ago
Gabriel Fair
1113
New contributor
Gabriel Fair is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
When I look at the Alnitak,the left most star of Orion's belt, it is 736 light years away. How could I convert this distance to an estimate of how long ago what I am seeing happened.
Would it be simply be 736 years ago?
Are there instances of when this isn't as straight forward?
distances space-time time
distances space-time time
asked 6 hours ago
Gabriel Fair
1113
New contributor
Gabriel Fair is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 6 hours ago
Gabriel Fair
1113
New contributor
Gabriel Fair is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 6 hours ago
Gabriel Fair
1113
New contributor
Gabriel Fair is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 6 hours ago
Gabriel Fair
1113
asked 6 hours ago
Gabriel Fair
1113
1113
New contributor
Gabriel Fair is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Gabriel Fair is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Gabriel Fair is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
For short distances (e.g. within our galaxy, or even within our local cluster of galaxies), this is an accurate method. It becomes inaccurate once the scale exceeds the point at which gravitational attraction is outweighed by the expansion of the Universe. As an extreme example, the Universe is roughly 46 billion light years in radius but light has only travelled for 13.8 billion years. Hopefully someone with greater expertise can post an answer about exactly how far away metric expansion of the universe becomes a significant factor.
– Chappo
3 hours ago
add a comment |Â
For short distances (e.g. within our galaxy, or even within our local cluster of galaxies), this is an accurate method. It becomes inaccurate once the scale exceeds the point at which gravitational attraction is outweighed by the expansion of the Universe. As an extreme example, the Universe is roughly 46 billion light years in radius but light has only travelled for 13.8 billion years. Hopefully someone with greater expertise can post an answer about exactly how far away metric expansion of the universe becomes a significant factor.
– Chappo
3 hours ago
For short distances (e.g. within our galaxy, or even within our local cluster of galaxies), this is an accurate method. It becomes inaccurate once the scale exceeds the point at which gravitational attraction is outweighed by the expansion of the Universe. As an extreme example, the Universe is roughly 46 billion light years in radius but light has only travelled for 13.8 billion years. Hopefully someone with greater expertise can post an answer about exactly how far away metric expansion of the universe becomes a significant factor.
– Chappo
3 hours ago
For short distances (e.g. within our galaxy, or even within our local cluster of galaxies), this is an accurate method. It becomes inaccurate once the scale exceeds the point at which gravitational attraction is outweighed by the expansion of the Universe. As an extreme example, the Universe is roughly 46 billion light years in radius but light has only travelled for 13.8 billion years. Hopefully someone with greater expertise can post an answer about exactly how far away metric expansion of the universe becomes a significant factor.
– Chappo
3 hours ago
add a comment |Â
1 Answer
1
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oldest
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up vote
4
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Yes, for stars in our galaxy, if a star is 736 light years away, the light took 736 years to reach here.
For very very distant objects, you need to account for the expansion of space. The light might have been travelling for 10 billion years, but in that time space has expanded and so the distance that you would find if you froze time and measured would be greater (to get the proper distance at the current time) it would be larger. This effect is not significant at distances less than about a billion light years.
answered 5 hours ago
James K
31k246104
+1, but since the OP seems to be interested in calculating lookback time, I think this answer would be more helpful if you gave the general relation between distance and lookback time / age of the Universe (just my opinion :) ).
– pela
29 mins ago
add a comment |Â
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
Yes, for stars in our galaxy, if a star is 736 light years away, the light took 736 years to reach here.
For very very distant objects, you need to account for the expansion of space. The light might have been travelling for 10 billion years, but in that time space has expanded and so the distance that you would find if you froze time and measured would be greater (to get the proper distance at the current time) it would be larger. This effect is not significant at distances less than about a billion light years.
answered 5 hours ago
James K
31k246104
+1, but since the OP seems to be interested in calculating lookback time, I think this answer would be more helpful if you gave the general relation between distance and lookback time / age of the Universe (just my opinion :) ).
– pela
29 mins ago
add a comment |Â
up vote
4
down vote
Yes, for stars in our galaxy, if a star is 736 light years away, the light took 736 years to reach here.
For very very distant objects, you need to account for the expansion of space. The light might have been travelling for 10 billion years, but in that time space has expanded and so the distance that you would find if you froze time and measured would be greater (to get the proper distance at the current time) it would be larger. This effect is not significant at distances less than about a billion light years.
answered 5 hours ago
James K
31k246104
+1, but since the OP seems to be interested in calculating lookback time, I think this answer would be more helpful if you gave the general relation between distance and lookback time / age of the Universe (just my opinion :) ).
– pela
29 mins ago
add a comment |Â
up vote
4
down vote
up vote
4
down vote
Yes, for stars in our galaxy, if a star is 736 light years away, the light took 736 years to reach here.
For very very distant objects, you need to account for the expansion of space. The light might have been travelling for 10 billion years, but in that time space has expanded and so the distance that you would find if you froze time and measured would be greater (to get the proper distance at the current time) it would be larger. This effect is not significant at distances less than about a billion light years.
answered 5 hours ago
James K
31k246104
Yes, for stars in our galaxy, if a star is 736 light years away, the light took 736 years to reach here.
For very very distant objects, you need to account for the expansion of space. The light might have been travelling for 10 billion years, but in that time space has expanded and so the distance that you would find if you froze time and measured would be greater (to get the proper distance at the current time) it would be larger. This effect is not significant at distances less than about a billion light years.
answered 5 hours ago
James K
31k246104
answered 5 hours ago
James K
31k246104
answered 5 hours ago
James K
31k246104
answered 5 hours ago
James K
31k246104
31k246104
+1, but since the OP seems to be interested in calculating lookback time, I think this answer would be more helpful if you gave the general relation between distance and lookback time / age of the Universe (just my opinion :) ).
– pela
29 mins ago
add a comment |Â
+1, but since the OP seems to be interested in calculating lookback time, I think this answer would be more helpful if you gave the general relation between distance and lookback time / age of the Universe (just my opinion :) ).
– pela
29 mins ago
+1, but since the OP seems to be interested in calculating lookback time, I think this answer would be more helpful if you gave the general relation between distance and lookback time / age of the Universe (just my opinion :) ).
– pela
29 mins ago
+1, but since the OP seems to be interested in calculating lookback time, I think this answer would be more helpful if you gave the general relation between distance and lookback time / age of the Universe (just my opinion :) ).
– pela
29 mins ago
add a comment |Â
Gabriel Fair is a new contributor. Be nice, and check out our Code of Conduct.
Gabriel Fair is a new contributor. Be nice, and check out our Code of Conduct.
Gabriel Fair is a new contributor. Be nice, and check out our Code of Conduct.
Gabriel Fair is a new contributor. Be nice, and check out our Code of Conduct.
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For short distances (e.g. within our galaxy, or even within our local cluster of galaxies), this is an accurate method. It becomes inaccurate once the scale exceeds the point at which gravitational attraction is outweighed by the expansion of the Universe. As an extreme example, the Universe is roughly 46 billion light years in radius but light has only travelled for 13.8 billion years. Hopefully someone with greater expertise can post an answer about exactly how far away metric expansion of the universe becomes a significant factor.
– Chappo
3 hours ago